ath10k-firmware: removed broken submenu

this package references an undefined variable for its submenu.
Remove this NOP variable assignment.

Signed-off-by: Alberto Bursi <alberto.bursi@outlook.it>

package/firmware/ath10k-firmware/Makefile

@@ -25,7 +25,6 @@ include $(INCLUDE_DIR)/package.mk
 define Package/ath10k-firmware-default
   SECTION:=firmware
   CATEGORY:=Firmware
-  SUBMENU:=$(WMENU)
   URL:=$(PKG_SOURCE_URL)
   DEPENDS:=
 endef